1. Field of the Invention
The present invention relates to a process for producing an ink jet head for discharging ink which is used in an ink jet printing system. More particularly, the present invention relates to a process which enables one to efficiently form a precise ink pathway with no deformation for an ink jet head and to attain the mass-production of a high quality ink jet head at a high yield by way of a process for producing an ink jet head which includes the steps of forming a photosensitive resin layer capable of contributing to the formation of an ink pathway on a substrate for an ink jet head, forming a coating resin layer on said photosensitive resin layer, and removing a predetermined ink pathway-forming portion of said photosensitive resin layer by way of elution to form an ink pathway.
2. Related Background Art
There are known a number of ink jet heads used in an ink jet printing system (or a liquid jet recording system) for performing printing. These ink jet heads are usually provided with a discharging outlet (which will be hereinafter occasionally called an orifice) for discharging printing liquid (ink), an ink pathway communicated with said discharging outlet and an energy generating element for generating energy utilized for discharging said ink.
As for the production of such ink jet head, there is known a process wherein fine grooves for the formation of ink pathways are formed at a given plate made of glass, metal or the like by way of cutting processing or etching processing, and the plate having the thus formed fine grooves is joined with a substrate for an ink jet head which is provided with discharging energy-generating elements to form ink pathways. However, as for this process for the production of an ink jet head, there are such problems as will be described as follows. In the case where the formation of said fine grooves is by way of the cutting processing, problems entail in that it is difficult for each of the fine grooves to have a smooth inner wall face, a crack or/and breakage are liable to occur at the plate, and therefore, a desirable yield cannot be attained. In the case where the formation of said fine grooves is by way of the etching processing, problems entail in that it is difficult to attain a uniformly etched state for all the fine grooves obtained, and the process for practicing the etching processing is complicated, resulting in an increase in the production cost. Therefore, there is a tendency for ink jet heads produced according to the above process for the production of an ink jet head to be varied in printing characteristics and therefore, the above process for the production of an ink jet head is difficult to stably mass-produce a desirable ink jet head having ink pathways having a uniform pattern at a high yield. In addition, as for the above process for the production of an ink jet head, there is also a problem in that upon joining the plate having the fine grooves with the substrate for an ink jet head, precise positioning between the two members cannot be easily conducted. Consequently, the above process for the production of an ink jet head is not suitable for the mass-production of a high quality ink jet head at a high yield.
In order to eliminate the problems in the foregoing process for the production of an ink jet head, U.S. Pat. No. 4,450,455 (hereinafter referred to as document 1) discloses a process for the production of a liquid jet recording head (that is, an ink jet head) which comprises providing a substrate for an ink jet head which is provided with energy generating elements disposed thereon, forming a dry film composed of a photosensitive resin material on the substrate for an ink jet head, forming grooves for the formation of ink pathways at the dry film by way of photolithography, joining a top plate made of glass or the like to the substrate for an ink jet head which is provided with the grooves using an adhesive to obtain a joined body, and mechanically cutting an end portion of the joined body to form discharging outlets, thereby obtaining an ink jet head.
The process for the production of an ink jet head described in document 1 has advantages in that as the grooves for the formation of ink pathways are formed by way of photolithography, the grooves can be precisely formed as desired; and the joining of the substrate for an ink jet head to the top plate can be easily conducted without the necessity of severely positioning the two members since the grooves for the formation of ink pathways are previously formed at the energy generating elements-bearing substrate for an ink jet head prior to joining the substrate to the top plate. However, as for the process for the production of an ink jet head described in document 1, there are such disadvantages as will be described as follows: (1) in the step of joining the substrate for an ink jet head to the top plate, the adhesive is liable to get in the ink pathways formed, wherein there is a tendency for the resulting ink pathways to be deformed; (2) in the step of mechanically cutting the joined body in order to form the discharging outlets, a swarf caused during the mechanical cutting is liable to get in the ink pathways, wherein the resulting ink jet head is liable to suffer from clogging during the operation thereof for performing printing; and (3) since the ink pathway-forming portions of the joined body are caved, some of the discharging outlets formed by mechanically cutting the joined body are liable to be accompanied with a breakage.
Consequently, the process for the production of an ink jet head described in document 1 is also not suitable for the mass-production of a high quality ink jet head at a high yield.
In order to eliminate these problems, U.S. Pat. No. 4,657,631 (hereinafter referred to as document 2) discloses a process for the production of an ink jet head which comprises providing a substrate for an ink jet head which is provided with energy generating elements disposed thereon, forming a resin pattern (that is, a resin solid layer) composed of a solubilizable resin at a predetermined ink pathway-forming portion on the substrate for an ink jet head, forming a coating resin layer composed of epoxy resin or the like so as to cover the resin solid layer on the substrate for an ink jet head, hardening the coating resin layer, and removing the resin solid layer by eluting it to form ink pathways, thereby obtaining an ink jet head. In addition, U.S. Pat. No. 5,331,344 (hereinafter referred to as document 3) discloses a process for the production of an ink jet head which comprises providing a substrate for an ink jet head which is provided with, energy generating elements disposed thereon, forming a two-layered photosensitive layer comprising a first photosensitive layer and a second photosensitive layer on the substrate for an ink jet head, forming a latent image pattern for the formation of ink pathways at the first photosensitive layer while forming a latent image pattern for the formation of discharging outlets at the second photosensitive layer, and developing these two latent image patterns at the same time, thereby obtaining an ink jet head. Further, U.S. Pat. No. 5,458,254 (hereinafter referred to as document 4) discloses a process for the production of an ink jet head based on the process described in document 2 wherein an ionizing radiation decomposable photosensitive resin is used as the constituent resin of the resin pattern (the resin solid layer) in the process described in document 2.
In any of the processes described in documents 2, 3 and 4, a solubilizable resin layer is disposed at a predetermined ink pathway-forming portion on the substrate for an ink jet head and a coating resin layer is disposed on the solubilizable resin layer while maintaining the resin layer as it is, and the resin layer is removed by way of elution, wherein desired ink pathways can be precisely formed without being deformed and without the incorporation of an adhesive into the ink pathways which occurs in the case of the process for the production of an ink jet head described in document 1. Further, in the case where an end portion of the substrate for an ink jet head which is provided with the coating resin layer thereon should be mechanically cut as in the process described in document 1, since the solubilizable resin is charged in the ink pathway-forming portion, a swarf caused upon the cutting operation is prevented from getting into the resulting ink pathways and the resulting discharging outlets are prevented from suffering from a breakage.
In documents 2, 3 and 4, as the solubilizable resin, there is used a positive type resist in view of easiness for removal. The positive type resist is capable of forming a desired pattern by virtue of a difference between the solution velocity of an exposed portion and that of a non-exposed portion. In any of the processes described in documents 2, 3 and 4, the ink pathway-forming portion is subjected to exposure and thereafter, it is removed by way of elution.
In any of the processes described in documents 2, 3 and 4, the formation of the coating resin layer on the ink pathway-forming portion is conducted by way of so-called solvent-coating process. The solvent-coating process is conducted in a manner of dissolving a resin, which is to be applied onto an object, in a given solvent and applying the resultant liquid onto the object. The solvent-coating process is typically represented by spin coating process. The spin coating process has an advantage in that a film having a uniform thickness can be relatively easily formed.
Now, particularly in the process for the production of an ink jet head of a so-called side shooter type which has a discharging outlet above an electrothermal converting body as an energy generating element capable of generating energy utilized for discharging ink, said discharging outlet is formed at the coating resin layer and therefore, the thickness of the coating resin layer is an important factor of deciding the distance between the electrothermal converting body and the discharging outlet which governs the ink discharging characteristics of the ink jet head. In view of this, the formation of the coating resin layer in the production of a side shooter type ink jet head is usually conducted by the spin coating process.
In the case of forming the coating resin layer by the solvent-coating process, as the solubilizable resin layer, comprised of the positive type resist which corresponds to the ink pathway-forming portion, is previously disposed as above described, it is important to pay careful attention to the solvent to be used. Particularly when as the solvent used in the solvent-coating process, a solvent having a excessively strong dissolving power is used, there is a tendency in that the exposed portion of the solubilizable positive type resist is dissolved while the non-exposed portion thereof is partly dissolved, wherein the resulting ink pathways are liable to be accompanied with a deformation.
By the way, in order to form a film on a substrate for an ink jet head at a uniform thickness by the solvent-coating process (that is, the spin coating process), it is necessary to properly adjust the evaporation rate and viscosity of a solvent used. As the film thus formed in the ink jet head field, it is usually made to have a thickness which is thicker than that of a film formed in the semiconductor device field. Therefore, in order to form such thick film at a uniform thickness in the ink jet head field, related film-forming conditions are necessary to be more severely controlled in comparison with the case of forming the film in the semiconductor device field.
As the thickness of the coating resin film governs the discharging characteristics of the resulting ink jet head as above described, the adjustment of the evaporation rate and viscosity of the solvent used eventually affects the yield of an ink jet head obtained. Particularly the use of a solvent having a low evaporation rate can easily attain the formation of a film at a uniform thickness. However, solvents having a low evaporation rate are mostly strong in dissolving power. In the foregoing conventional processes for the production of an ink jet head, when a solvent having a strong dissolving power is used upon the application of a given resin for the formation of the coating resin layer, a deformation is liable to occur at the resulting ink pathways, resulting in reducing the yield of an ink jet head obtained. This situation makes it difficult to attain an improvement in the productivity of an ink jet head.
Consequently, in accordance with any of the conventional processes for the production of an ink jet head which includes the steps of forming a photosensitive resin layer contributing to the formation of an ink pathway on a substrate for an ink jet head, forming a coating resin layer on the photosensitive resin layer, and removing a predetermined ink pathway-forming portion of the photosensitive resin layer by way of elution to form an ink pathway, there is a problem in that it is difficult to efficiently form a precise ink pathway with no deformation for an ink jet head and to attain the mass-production of a high quality ink jet head at an improved yield.
The present inventors conducted extensive studies through experiments in order to solve the foregoing problems in the prior art and in order to attain a process which enables one to effectively form an ink pathway with no deformation even when a solvent having a strong dissolving power is used upon forming the coating resin layer by way of the coating process, and to mass-produce a high quality ink jet head at an improved yield.
As a result, there was obtained the following finding. That is, when a photosensitive layer composed of an ionizing radiation decomposable photosensitive resin containing a crosslinkable structural unit is formed at a predetermined ink pathway-forming portion on a substrate for an ink jet head, the photosensitive layer is crosslinked, a coating resin layer is formed on the crosslinked photosensitive layer, and ionizing radiation is irradiated to a predetermined portion of the crosslinked photosensitive layer which contributes to the formation of an ink pathway through the coating resin layer, the above aims can be effectively attained as desired. The present invention has been accomplished based on this finding.
An object of the present invention is to provide a process which enables one to efficiently produce a high quality ink jet head having a highly precise ink pathway at a high yield.
Another object of the present invention is to provide a process which enables one to efficiently produce a high quality ink jet head having a highly precise ink pathway with no deformation at a high yield even when the coating resin layer is formed by the coating process while using a solvent having a strong dissolving power.
A further object of the present invention is to provide a process which enables one to efficiently produce a high quality ink jet head having a highly precise ink pathway at a high yield without a substantial limitation for the resin by which the coating resin layer is constituted and also for the solvent used upon forming the coating resin layer by the coating process.
A still further object of the present invention is to provide a process which enables one to efficiently produce a high quality ink jet head having a highly precise ink pathway at a high yield while easily attaining uniformity for the thickness of the coating resin layer.